Induction heating furnace



Jan. 26, 1954 L. DREYFUS TAL INDUCTION HEATING FURNACE 5 Sheets-Sheet 1Filed Dec. 29, 1950 SS m ,m

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INDUCTION HEATING FURNAUE Filed Dec. 29, 195o s sheets-sheet s Jan. 26,1954 L. DREYFUS ETAL INDUCTION HEATING FURNACE 5 Sheets-Sheet 4 FiledDec. 29, 1950 Jan. 26, 1954 DREYFUS ETAL 2,667,524

INDUCTION HEATING FURNACE Filed Deo, 29, 1950 5 Sheets-Sheet 5 PatentedJan. 26, 1954 INDUCTION HEATING FURNACE,

Ludwig Dreyfus, Thor Thelemarck, Ivar Beckius,

and Hugo Lindstrm, Vasteras, Sweden, assign,.- ors .to Allmanna SvenskaElektriska Aktieholaget, Vasteras, Sweden, a corporation of SwedenApplicationecember 29, 1950, Serial No.203,255

Claims priority, application Sweden January 14, 1950 7 Claims.

Eddy current furnaces for heating rolled stuff or ingots which have tobe fed in a continuous sequence through a heating chamber seldom arearranged as cross field furnaces, since the use of cross eld furnacesfor this purpose involves certain drawbacks. This will be evident fromthe following argumentation with reference to the accompanying Figs.latv and 1b. showing the conventional cross field furnace. This is aneddy current furnace in which the main direction l (see Fig. la) of thefield is perpendicular tothe longitudinal extension of the coil. Theactive portion of the furnace consistsk of the coil 2., the longitudinalsides 2 of which are parallel to the longitudinal direction of thearticle 3 tov be treat ed, while the short sides 2* are substantially atright angles to the longitudinal sides even though often in a higher orlower plane for not being in the way of the charge 3. while fed in andout. If the coil is surrounded by a. closedv laminated' yoke 4 whichconfines a furnace space of rectangular section, the cross field l willhave approximately the same intensity all over the void furnace spacewhich, of course, is advantageous, because in a homogenous alternatingVfield articles of rather different cross sections and' thickness. may beheat-treated.

However, this construction has, as mentioned above, some drawbacks. Thevoltage of the furnace is proportional to the fiux in the furnace space.and in the most usual design of the fur. nace as a high frequencyfurnace with full skin effect within the charge the interior of thecharge is practically free from field. The greater the width A of thecharge is at right4 angles to the direction of the iield the smallerbecomes the flux within the furnacel chamber at a given intensity offield, and the lower becomes therefore the voltage ofl the coil of thefurnace for a given current. But the product. of the current andA thevoltage of the coil is equal to the power of the condenser battery.Therefore, the paradoxical result is: obtained that the smaller theweight per meter of the ingots or rolled stuff, the greater must be thecondenser battery to be switched in parallel to one andthe same furnace.Since this is unecomonical, one and the same furnace can only be usedfor a very limited range of magnitude of the articlestov be treated'.

Another drawback is that in a cross eld furnace according to Figs. 1aand 1b4 the whole weight of the charge must be borne bythe furnacechamber which also has to be lined with a mufile 5 of heat. insulatingceramic material. The roof and the bottom ofthl's. munie, however.

cannot be made thick', for this would involve an increase of the pathof. the cross.: field. which would require a greater number of ampereturns and therewith greater current losses due to the heat within thefurnace coil. Heat insulating materials, however, are not particularlylasting, so that the lining soon becomes worn as heavy articlescontinuously are fed: in and out or through the heating chamber..

The object of thev present invention is a cross eld furnace which doesnot have the above men.- tioned disadvantages. The principal feature ofthe invention is that the bottom. of theV heating chamber is replaced bya feeding. means of heat resisting steel and lifted into thealternating, iield itself in an embodiment which will be describedlater, and that the longitudinal sides of the furnace coil are mademovable horizontally relative to one anotherv in. suchv a manner thatthey minimum horizontal distance between the. vertical longitudinalsides of. the coil and articles of different size can be maintainedsubstantially constant.

The invention willnow be described with reference to the accompanyingdrawings; whereon:

Figs. la and 1b show schematically sectional views of a. furnace knownheretofore.v

Figs. 2aand 2b. each shows a sectional view of one half of a furnaceaccording to. the present, invention with work-pieces: of differentdimensions.

Figs. 3c, 3b and 3c show in three. sectional viewsr an example of theend connections. of the. heating conductors according to. thisinvention.

Figs. 4a, 4b and 4c show in three sectional views another example. ofthe end connectionsY of heating conductors according to this invention.

Fig. 5 is a perspective View showing a part. of the conveyor meansaccording to this invention.

Fig.` 6 is an end view of the, furnace., showing a modified form ofconnections.

In Figs. 2a and 2b there, is shown schematically a furnace according tothe invention, Wherein Fig. 2a showsy one half of the furnaceaccommodating within the field a minor article, Whereas Fig. 2b showsthe same half of the furnace with a major article lying within thefield. Thev upper part of the figures shows the distribution of theiield as long as the articles are magnetic., while the lower part ofthe. figures illustrates the distribution of the eld the. articleshaving become so warm that theyl become unmagnetio. In Figs. 2a and2bthe articles have square cross; sections andA different` side lengthsbut'thef same dis,- tance a' from the longitudinal sides 2.v adjacentthe coil. The articles rest on transport or conveyor means 6 consistingof U-shaped bails 6a of heat resisting. sheet, the sides of which arestayed by cross plates 6b. These bails are conducted between the sideyokes 4 on a conveyor means indicated schematically in Fig. 5, which isarranged in such a manner that the bails may be advanced that thedistance a' and a, respectively, between I the vertical side surfaces ofthe coil and the yokes and the article 3 to be treated remainapproximately constant. The diagrams of lines of force show that in thiscase also the same coil reactance may be expected in all charges.Therefore the both diagrams of `magnetic fields in the first heatinginterval, where the charge is still magnetic, show equal partial fluxesA I per half the cross section of the furnace and equal partial iiuxesA@ in the second heating interval beyond the magnetic transformationpoint where the charge becomes non-magnetic. In the use of stationarycoil sides and side yokes as shown in Figs. 1a and 1b, the number of thepartial fluxes would have been 30-40 per cent greater at the minor crosssection of the article, and the power of the condenser battery wouldhave been increased in the same degree for the same current through thecoil, i. e. for the same field intensity.

Figs. 3a, 3b, 3c, 4a, 4b, and 4c illustrate in three views at rightangles to each other partly in section two different constructions ofthe short sides of the coil enabling the displacement of thelongitudinal sides and yokes. Now the problem arises not only to securea reliable electrical contact for each one of the numerous turns of thecoil despite of their movability but also to bring the indispensableartificial cooling so close to the ends of the coils that theirover-temperature, despite of the high density of current occurringalways in high frequency furnaces, is held within allowable limits.

In the arrangement according to Figs. 3a, 3b and 3c, the mutualmovability of the coil sides is obtained in that the upright tubularconductors 22 of the coil are joined on one side thereof with doublehorizontal contact bars 23, between which single contact bars 24 intrudeas a continuation of opposite upright conductors. The coil ends formedby these contact bars engaging each other are isolated from each otherby the intermediance of sheets of insulating material 25. The bars 2sand 24 have longitudinally extending holes made therewithin and are heldpressed against each other by a bolt I with a wing nut II. The coolingwater is passed from turn to turn by means of rubber tubes 2s fixed bynipples 21. Y

In the arrangement according to Figs. 4a, 4b and 4c, the connectionbetween the longitudinal sides is made by `means of superflexible coppercables I5 (fiat or round so called stranded wires). The fixtures of 4theflexible conductors are hard soldered directly on the heads I8 traversedby the coolingwater, to which heads the conduc-` tors of thelongitudinal sides are connected. The cooling 4wateris led `from turntoLturn by means 4 of nipples I9 and rubber tubes I6. In the occurrenceof long coil ends, it may be necessary to place the stranded copper wireI5 within the rubber tubes I6 as shown, for example, at Fig. 6 in whichthe conducting cables I5 are enclosed within the flexible rubber tubesI6.

It will be seen, when comparing Figs. la and 1b with Figs. 3a 3b and 3cand Figs. 4a, 4b and 4c, that the yoke and muflie of the conventionaliield furnace have been broken up, not only over the little distancewhich is required for making the side yokes movable, but over such agreat distance that theweight of the charge not at all will load theVconstruction of the furnace itself. Instead, the chargeis supported andtransported according to the invention by a feeding means of heatresisting steel so that all previous trouble with the wear of ceramicsupport is avoided. It is true, this metallic support has to be liftedinto and placed within the very Zone of the cross field, but, accordingto the invention, this may be carried out in such a manner that itnevertheless only involves eddy current losses not worth mentioning.

In Fig. 5, two of the bails are shown in detail, which bails serve forthe support of the articles while travelling through the furnace. Thesebails are supported by cross beams I below the furnace which areadvanced belowv the furnace by conveyor chains 20 which run on bars 2 I.The transport means Vmay be made movable in vertical direction relativeto the yokes or vice Versa. The arrangement for effecting such movementis not shown on the drawings but it will be noted from a comparison ofFigs. 2a and 2b that the spaces between the yokes and the conveyor meansare different, indicating that these two means are movable with respectto each other in a vertical direction. These bails are formed andorientated within the alternatingeld in such a manner that the latternowhere has to cross any surfaces of considerable width at a right angleto the direction of the field. Therefore, the side pieces 6a consist ofso narrow lamellae, that the f field in theselamellae cannot produce'anyeddy current losses worth mentioning. The same applies to thecross-plate 6b within the middle plane of the furnace, which is known tocoincide there with the direction of the lines of force. Finally, thebottoms 6c of the bails are drawn` downwards-below the lowermost edge ofthe side yokes-to such an extent that they travel within a very feeblealternating field, the direction of Whichbesides does not much differfrom the plane of the bottoms. As a conclusion, the construction of thelinks may be described as consisting of a cross-plate in the middlehaving two semi-opened pockets on both sides, the lines of forceof thefield'entering and leaving these pockets without crossing the limitingsurfaces of the pockets in a degree worth mentioning. By this shaping,it has Ybeen possible to enable the links without intermediance ofceramic material to support directly the charge and to place hardwearingtransport means substantially free from losses withinl the 'heatingchamber itself.` Of course therewill be nothing to'prevent the insertionof aceramic piecebetween the links and the charge, if this` should berequired. In a furnace having movable side yokes the Awidth of the linksof course has to be adapted to the distancer of the side yokes forheating the narrowest articles for which the furnace is designed. Weclaim as our invention: v1 ;Aninduction furnace for heating metallicarticles while such articles are being fed successively and continuouslytherethrough, comprising two longitudinally extending laminated ironyokes arranged in spaced relation to each other, hollow duid-cooledcurrent conductors located in slots in said yokes, means for moving theyokes towards and away from each other in accordance with the differentwidths of the articles being treated, means located outside and abovethe space between said yokes for connecting the ends or said conductors,conveying means for the articles being treated, said means being adaptedto travel at different levels with respect to the yokes in accordancewith the different heights of the articles being treated, and means forsupporting the articles being treated, the said supporting means beingiiXed to said conveying means and being adapted to project from belowvinto the space between the yokes, and said supporting means consistingof bails formed Vby U-shaped bent sheets of heat resisting material withupwardly extending legs stayed by cross pieces located between such legsin such a position that the side surfaces and the bottoms of said bailsare substantially parallel to the direction of the alternating currentield between the yokes for preventing eddy currents in said bails.

2. An induction furnace for heating metallic articles while sucharticles are being fed successively and continuously therethrough,comprising two longitudinally extending yokes of magnetic materialarranged to form therebetween a space for the passage of the articlesbeing treated, means for moving said yokes towards and away from eachother, slots in said yokes, hollow current conductors located in saidslots, bars located outside and above the space between said yokes andattached to the ends of said hollow conductors to electrically connectthe conductors within one of the yokes with the conductors within theother yoke, means for insulatingly and movably holding the barstogether, and flexible insulating pipe means also located outside andabove the space between the yokes for the passage of cooling uid betweensaid conductors.

3. An induction furnace for heating metallic articles while sucharticles are being fed successively and continuously therethrough,comprising two opposed longitudinally extending laminated yokes ofmagnetic material arranged to form therebetween a space for the passageof the articles being treated, means for moving said yokes towards andaway from each other, slots in said yokes, hollow current conductorsembedded within said slots, flexible conductors located outside andabove the space between said yokes and electrically connecting theconductors in the slots in opposed yokes, and flexible insulating pipemeans for interconnecting and conveying cooling iiuid between saidembedded conductors.

4. An induction furnace for heating metallic articles while sucharticles are being fed successively and continuously therethrough,comprising two opposed longitudinally extending laminated yokes ofmagnetic material arranged to form therebetween a space for the passageof the articles being treated, means for moving said yokes towardsandgaway from each other, slots in said yokes, hollow current conductorslocated in said slotsy flexible conductors located outside and above thespace between said yokes and electrically connecting the conductors inthe slots in the opposed yokes, and ilexible insulating pipe meansenclosing said exible conductors and supplying cooling i-luid to thehollow conductors in said slots.

5. An induction furnace according to claim l, comprising wedges ofrefractory material covering the hollow conductors within the slots insaid yokes.

6. An induction furnace according to claim 1, comprising hollow flexiblemeans for connecting the ends of said hollow conductors and for theconveyance of cooling fluid between said conductors.

7. An induction furnace according to claim 1, comprising insulatingflexible pipe means serving to convey cooling fluid from the currentconductors in one yoke to the current conductors in the other yoke, thesaid Vmeans for electrically connecting the ends of the hollowconductors being arranged within said insulating iiexible pipe means.

' LUDWIG DREYFUS.

THOR THELEMARCK. IVAR BECKIUS.

HUGO LINDSTRM.

References Cited in the le of this patent UNITED STATES PATENTS'- NumberName Date 1,807,147 Brooke May 26, 1931 1,813,591 Urey July 7, 19311,861,869 Long June 7, 1932 2,044,763 Bouton et al. June 23, 19362,052,010 Bailey Aug. 25, 1936 2,404,987 Rudd July 30, 1946 2,481,008Gagliardi et al. Sept. 6, 194:9 2,490,206 Calley Dec. 6, 1949 2,513,778Bailey July 4., 1950 FOREIGN PATENTS Number Country Date 523,785 GreatBritain July 23, 1940

